(1) Field of the Invention
This invention relates to an electrophotographic photosensitive material suitable for offset printing and lithography and a process for the preparation thereof. More particularly, the invention relates to an electrophotographic photosensitive material for offset printing and lithography in which a novel multi-layer distribution structure is formed in an intermediate layer interposed between a flexible substrate and a photoconductuve layer.
(2) Description of the Prior Art
Plates in which an oleophilic ink-supporting portion corresponding to an image to be printed and a hydrophilic ink-repelling portion corresponding to a non-image area, i.e., the background, are formed on a suitable water-resistant substrate have heretofore been broadly used for offset printing or lithography.
Further, processes for preparing these printing plates according to electrophotography have been known from old. According to these known processes, an electrophotograhic photosensitive material comprising a flexible substrate, an electroconductive back coat layer formed on one surface of the flexible substrate, an electroconductive intermediate layer formed on the other surface of the substrate and a photoconductive layer formed on the intermediate layer is passed through a series of the steps of charging, imagewise exposure, development and fixation to form a fixed image of toner particles on the photoconductive layer, and then the photoconductive layer of the photosensitive material is treated with an etching solution to render hydrophilic a fine powder of an inorganic photoconductor contained in the photoconductive layer, whereby an oleophilic ink-supporting portion corresponding to the area of the fixed image of toner particles and a hydrophilic ink-repelling portion corresponding to the non-image area are formed.
Known electrophotographic photosensitive materials, however, are still insufficient in a combination of the sharpness of an image and the resistance to the printing operation when they are used as plates for offset printing or lithography. For example, in order to form a clear and sharp toner image, the intermediate layer of an electrophotographic photosensitive material is required to be sufficiently electroconductive, but in order to improve the resistance to the printing operation, the intermediate layer is required to show a sufficient moisture-resistant adhesion at the etching or printing step. In general, resinous compositions having a high electroconductivity are poor in the moisture-resistant adhesion, whereas resinous compositions having a high moisture-resistant adhesion are poor in the electroconductivity. Accordingly, any of known resinous compositions can hardly satisfy the foregoing two requirements similtaneously.
In electrophotographic photosensitive materials heretofore used for production of plates for offset printing or lithography, a composition comprising (1) a cationic or anionic resinous conducting agent and (2) a water-soluble or water-dispersible resin is used as the resinous composition for the intermediate layer. However, this composition is still insufficient in the combination of the electroconductivity and the moisture-resistant adhesion.